1. Field of the Invention
The present invention is an electronic training device for activities where fore and aft foot balance is important and is particularly relevant to such activities where an audible indication of such balance is useful.
2. Discussion of Background and Material Information
Maintaining correct balance in the form of an athletic stance with the weight centered in the fore/aft direction is important in many athletic activities. In skiing, correct longitudinal balance is necessary to drive the forward inside metal edge into the snow in order to steer the ski through a carved turn. By maintaining pressure against the front of the boot, the skier's weight and isometric force from knee flexion is applied to the ski's carving edge. This action generates the pressure necessary to engage the forward metal edge of the ski into hard snow, thereby maintaining control of the ski. Other sports such as snowboarding, ice skating and in-line skating require similar forward balance.
Most novice and some moderately proficient skiers exploit the extended length of a ski behind the boot to successfully negotiate terrain with an incorrect stance, specifically a stance where excessive pressure is applied to the rear of the boot and consequently to the rear of the ski. As described by Witherell and Evrard in The Athletic Skier, this incorrect stance is made possible by the large amount of leverage provided by the rear section of the ski. This so-called "invisible foot" enables skiers to skid down steep slopes by dragging the tails of the skis against the snow. This method, while effective to a limited extent, is both incorrect and dangerous. The method is incorrect because the loss of forward pressure on the ski limits the amount of control available to the skier for steering, negotiating hard snow and for handling sudden increases in the pitch of the slope. The practice of leaning back on the skis is dangerous because loss of control from a rear-weighted position may result in the skier falling over the back of the skis. This form of accident has been known to sever the connection of the anterior cruciate ligament to the tibia, the most common form of injury in skiing.
The ability to apply correct forward pressure to a ski is a difficult skill to learn because it runs counter to the defensive instinct of leaning backward when encountering a steep or icy slope. Beginning skiers have difficulty mastering the concept because much practice is required to develop a feel for correct balance on a ski on slopped terrain. Even advanced racers have difficulty maintaining the skill at high speeds on a difficult race course. The undesirable trait of leaning back on the skis is known in the race community as "riding in the back seat."
Traditional ski instruction methods are not suitable for overcoming this problem. Skiing balance is particularly difficult to observe when a skier is headed downhill because the force vector generated by gravity on a skier's center of mass does not pass through the skier's boots. It is difficult for an athlete or a beginner to know when the correct weight is being applied because no direct measurement exists. Specifically, no device exists to continuously monitor the correct forward pressure of an athlete while skiing down a hill.
Similar advantages accrue to the snowboarder, ice skater or in-line skater who maintains a correct forward stance in these sports. In each case a loss of control and potential hazard exists when the athlete succumbs to the defensive instinct of learning back in a defensive posture.
Various methods of measuring and monitoring the performance of an athlete in a laboratory setting are known in the art These devices use mechanical and electrical means to measure the dynamics of runners, skiers and other athletes. These tend to use force pads, or sensors with wires running from the test subject to static laboratory equipment. The use of video analysis is also extensively documented.
U.S. Pat. No. 5,221,088 to McTeigue, et al. describes means for measuring weight distribution in sports such as golf or baseball where the athlete engages in a static stance before swinging an object at a ball. Sensors in each shoe produce a signal proportional to the amount of weight placed thereon. The signals are sent to a computer which compares each against a separate predetermined range of values. This predetermined range is a selectable percentage of a maximum value, which is calibrated to a person's weight. Various audio signals are generated in response to the comparison to provide feedback for a variety of training algorithms. The usefulness of this device for measuring weight distribution among different sensors in a single shoe is noted.
Marsh describes in U.S. Pat. No. 5,471,405 a device to record forces applied to garments including shoe soles, shoe liners and gloves. A weight sensor in each shoe is constantly sampled and the data is wirelessly transmitted to a display processor unit Information on the intensity and duration is provided to the user, such as a runner or golfer.
U.S. Pat. No. 4,516,110 issued in May 1985 to Overmyer describes a method of measuring the relative bend of the front and rear portions of a ski by the use of strain gages which are bonded to those portions of a ski. The Overmyer device is self-contained on the athlete, with means to provide continuous feedback during a skiing performance without external observation or equipment.
Static devices applicable to teaching a skiing stance are described in several patents. U.S. Pat. No. 4,092,787 issued to Kaempfen describes a static fixture for practicing ski turns. Campbell, III in U.S. Pat. No. 4,694,684, describes a static fixture for measuring the longitudinal balance point of a specific skier on a specific pair of skis intended for use in refining the location of the binding position.
U.S. Pat. 4,813,436 issued to Au describes a system capable of monitoring the amount of pressure simultaneously exerted on a plurality of sensors by the sole of a person's foot and simultaneously displaying those forces while the person uses a treadmill.
Ratzlaff et al in U.S. Pat. No. 4,814,661 describes a system for measuring forces generated by the plantar surface of a human foot using several piezoelectric transducers located under the foot and including means for displaying the instantaneous forces simultaneously measured.
Several additional patents describe methods for enclosing force measurement instrumentation on a shoe. U.S. Pat. No. 4,649,552 issued to Yukawa describes an electronic pedometer where a step sensor in the sole of a shoe triggers a counter unit mounted on the laces. U.S. Pat. No. 4,703,445 issued to Dassler describes a sensor for measuring the speed of and distance covered by a running shoe. U.S. Patent No. 5,323,650 issued to Fullen et al describes the use of a sensor array embedded in a shoe sole for measuring forces applied to specific locations of the foot with greater resolution. The invention of Thomas et al in U.S. Pat. No. 5,253,654 uses a strain gage mounted in a shoe to monitor the weight applied to a lower extremity for orthopedic purposes.
Several other patents describe sensors applicable to human force measurement. In U.S. Pat. Nos. 4,734,034 and No. 4,856,993 both issued to Maness et al, means are described to measure points of contact in dental occlusion. Podoloffet al in U.S. Pat. No. 5,033,291 describes a flexible sensor for uses in applications where shear forces are encountered and sensor thickness is a consideration.